This invention relates to power transmission belts and more particularly to multi-ribbed power transmission belts for use with multi-grooved sheaves or pulleys in heavy duty type drives. The invention relates specifically to an improved belt of this type having a more unitary structure for the transmission of power at low tensions. The invention also relates to the method of making the improved belt.
Multiple ribbed or grooved power transmission belts in the prior art have essentially taken two basic forms. In one a plurality of individual V-belt sections of essentially trapezoidal cross-section have been bonded together by means of a flexible tie band of rubber and fabric. Each of the individual V-belts include a reinforcement usually in the form of stress-resisting cords composed of such materials as cotton, nylon, rayon, polyester, wire, glass, or any other suitable material well known in the art. Typical of this type belt are those disclosed in U.S. Pat. No. 2,263,960 to Wilson, U.S. Pat. No. 3,404,577 to Zahn, U.S. Pat. No. 3,523,461 to Nemecek et al., and U.S. Pat. No. 3,564,933 to Clinkenbeard.
In another form the multiple ribbed belts are essentially flat power transmission belts having a plurality of longitudinally extending substantially V-shaped or trapezoidal-shaped ribs molded or cut on the inner surface thereof. The ribs are intended to mate or register in correspondingly aligned V-shaped pulley grooves. In this type belt the reinforcing cords are disposed above the ribs. U.S. Pat. No. 2,728,239 to Adams Jr. and U.S. Pat. No 2,802,511 to Waugh are typical of this latter type multi-ribbed belt.
The prior art belts have not been entirely satisfactory for the purpose intended. For example, when individual molded V-belts have been tied together there has been a tendency to create variances in the cord line in each rib and from rib to rib, thus causing differential driving tendencies of the banded belts since the neutral axis or cord line in each belt is in a slightly different location with respect to the top or bottom surfaces of the belt. Also, in the type of multiple ribbed belt in which the cord line is disposed above the ribs, each individual rib is not capable of the traditional V-belt wedging action in the pulley grooves. This is the case since the cord tensile member is not located in each individual rib and no clearance spaces are provided between the multi-grooved pulley and the belt thereby not allowing individual wedging action to occur.
The beforementioned disadvantages of the prior art multi-ribbed or multi-grooved belts are overcome by the belt structure of the present invention which will be hereinafter fully described.